Magnet clamp for an apparatus for indicating an electrically grounded condition



Jan. 4, 1966 z. WALSH 3,227,988

C. MAGNET CLAMP FOR AN APPARATUS FOR INDICATING AN ELECTRICALLY GROUNDED CONDITION Original Filed Feb. 13, 1961 2 Sheets-Sheet 1 ill Jan. 4, 1966 c. z. WALSH 3,227,988

MAGNET CLAMP FOR AN APPARATUS FOR INDIGATING AN ELEGTRICALLY GROUNDED CONDITION Original Filed Feb. 13, 1961 2 Sheets-Sheet 2 l l I l i I United States Patent 1 Claim. 01. 339-12 This application is a division of my copending application for patent, Ser. No. 88,937, filed February 13, 1961, now abandoned.

This invention relates generally to a means for indicating the grounding of an electrostatically charged member,'e.g., a tank truck which transports volatile petroleum products, and specifically to an attaching means for such an apparatus.

Many tests indicate that the majority of tank truck transporters entering a petroleum products loading rack carry a substantial electrostatic charge, which, if not dissipated before the loading procedure begins, may cause a fire or explosion, should there be a static discharge during the loading of the products. This discharge may occur between the loading spout and the opening of a tank compartment, or between the rack structure or an individual contacting the truck transporter to result in the ignition of vapors within the truck transporter or of those vapors flowing to the ground.

A static charge can be accumulated also by the flow of petroleum products into the tank truck transporter compartments during the loading period. If such a charge is not drained off continuously through an electrical grounding arrangement, it may build up to a point where it will discharge to ground and result in an explosion and/ or fire.

Accordingly, it is an overall object of the present invention to provide an improved means for dissipating the electrical charge which may exist on a tank truck transporter at the time it enters the loading rack or which may develop during its loading operation.

Another object of the invention is to provide an improved electrical grounding arrangement which is dependable and indicates that the electrical circuit to ground is not interrupted.

Still another object of the invention is to provide an effective electrical grounding circuit with means for indicating when such a circuit is broken.

Another object of the invention is to provide an electrical ground indicating apparatus which is simple to construct and economical to operate.

And another object of the invention is to provide an improved means for interconnecting an electrical ground indicating apparatus with an electrically charged member,

These and other objects, advantages and features of the invention will become apparent from a consideration of the specification in the light of the figures of the accompanying drawings wherein:

FIG. 1 is a simplified showing of the basic circuit of my electrical ground indicator;

FIG. 2 is a showing of a refinement in the circuit of the ground indicator disclosed in FIG. 1;

FIG. 3a is a perspective view of a magnetic grounding clamp for use with my electrical ground indicating apparatus;

FIG. 3b is a sectional view of the grounding clamp taken along the line 3b3b of FIG. 3a; and

FIG. 4 is a diagrammatic disclosure of the installation of the electrical ground indicator.

The objects of my invention are achieved by the use Patented Jan. 4, 1966 of relay control means which, in response to the completion of an electrical circuit to ground by the attachment of the magnet clamp to the charged member, actuates a circuit to indicate the electrically grounded condition.

Referring to FIG. 1, there is disclosed the basic circuit of my electrical ground indicator, including a transformer at 10, with its primary winding at 11 furnished with power by connection at the terminals 12 and 13, such power being obtained from a source of volt, 60 cycle alternating current. The secondary winding 14 of the transformer 10 steps down the 120 V. AC. supply to a nominal voltage of approximately 5 volts, with one terminal of the secondary winding grounded at the terminal 15, while the other terminal is connected in series with a resistor 16, a relay coil 17, and a terminal at 18. A grounding clamp (not shown), adapted to be attached to the member or object to be electrically discharged to ground, is connected across the terminals 15 and 18. In response to the flow of current when the ground circuit is completed by attachment of the clamp to the member to be electrically discharged and across the terminals 15 and 18, the relay coil 17 actuates the relay switch 19 in the indicating circuit, shown generally at 20, which has a lamp 21 in series therein and is connected across the source of power for the transformer, at 12 and 13. It is possible to replace the lamp by other indicating means, as, for example, audible means such as a buzzer or a bell, or an electrical set up for closing down the operation of the loading pump.

There is disclosed in FIG. 2, a refinement of the basic electrical ground and indicating circuit of FIG. 1, to include an explosion proof container 22, and with the same enumeration for the same or similar elements disclosed in FIG. 1. These include a hermetically sealed transformer at 10, indicated by the dotted outline, with the same 120 V. AC. power supply to the primary winding 11 and across which the indicating circuit 20 is shown connected at 12 and 13'. The secondary winding 14 of the transformer 10 is connected at one of its terminals to ground, as at 1511, while the other terminal is connected in series to a resistor 16, a rectifier 23, and a contact 24. The series circuit is continued therefrom through one of a pair of conductors at 25, which conductors are joined to conductor rods of a magnet clamp 30. The free end of the other of the pair of conductors is connected to the ground at 15b. The relay coil 17 is connected to the output of the rectifier 23 and actuates the relay switch at 19 to complete the indicating circuit 20 with the lamp at 21. In conjunction with the conductors 25, there is disclosed a take up reel 25a on which the excess of the pair of conductors may be stored. The combination of the rectifier, relay coil and switch may be positioned in a sealed container, shown in dotted outline.

Referring to FIGS. 3a and 3b, the magnet clamp 30 consists of a pair of contact point assemblies 31 which are unitized by a pair of yokes 32, joined together by threaded means, e.g., a nut and bolt assembly at 32a, and a carrying handle 33 joined to said yokes. Each contact point assembly consists of a cylindrical permanent magnet 34, with an axial bore 34a, housed in a Bakelite sleeve 35. The axial bore 34a receives the conductor rod 36 of T-shape configuration and is preferably bronze, with a stellite contact point at 36a at the T-end, with this end of the rod working in an appropriate shaped slot 34b in the magnet 34. The rod 36 is kept in resiliently mounted assembly by the screw nut and washer, at 37a and 37b respectively, and the loading springs at 38a and 38b. One end of each of the conductors 25 is fastened to an end of each plunger rod 36 of the assemblies 31, and is shown soldered at 39, although other fastening means could be used as a terminal connection to receive the conductor ends, for ease of maintenance.

In use, the magnet clamp is placed on the tank transporter to be loaded, and normally the indicating circuit will light up showing that there is a good contact and that the transporter is grounded. If there is no lighting (or other indication), slight movement of the clamp will cause the contact points to dig through paint or dirt to obtain a good contact and so lead to an indication of grounding. In case the tank transporter is made of aluminum or other non-ferrous material, the weight of the magnet clamp is enough to make contact through the points 36a, and usually dome cover assemblies are constructed of a ferrous material to which the magnet clamps will hold. With this type of clamp, positive disengagement, because of careless loading, is unnecessary.

In operation, the electrical ground cricuit is completed by the application of the magnet clamp 30 to the member to be grounded, e.g. the magnets 34 are positioned to engage a part of a tank truck 26 or rest thereon. When the contact point engagement is made, a minute amount of current (of about .0015 ampere) flows from one contact point of the clamp through the portion of the truck or other member to be grounded and out of the other contact point of the clamp through one of the pair of conductors to the ground connection at 15b. The small amount of current flow causes the relay to operate, closing the switch at 19, completing a circuit and so energizing the indicating means to show that an electrical ground has been established. With the low voltage of approximately 5 volts and the small amount of current drawn by the relay, it is virtually impossible to obtain a. spark when making or breaking the contact with the truck. As mentioned for FIG. 1, the relay coil may be utilized in a control scheme to interlock the operation of a solenoid valve to prevent the loading operation from taking place unless the truck has been grounded electrically.

As disclosed in FIG. 2, there are separate ground contacts at a and 15b, respectively for one end of the secondary winding of the transformer and for one of the pair of conductors in order to assure the complete electrical grounding of the charged member, even though it may be possible to interconnect the ground connection as indicated by the dotted line at 150.

FIG. 4 is a diagrammatic showing of the installation of my improved electrical ground indicator at a loading rack. The ground indicator in its explosion proof container is at 22, With the indicating light or other means at 21, the double conductors at 25, with the take up reel at 25a, and the magnet clamp at 30 for engagement with a tank truck, e.g. 26.

Thus there has been shown and described a device for obtaining a reliable static ground on a tank truck or other device which contains volatile products and is capable of building up an electrical charge, with an indication that an electrical ground connection has been made before tank filling operations are started and while filling operations proceed.

Other modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claim.

I claim:

In a series circuit for grounding an electrostatically charged body, the improvement comprising means for attachment to said charged body for completing said series circuit to ground therethrough, said means for attachment including a pair of contact point assemblies and means for joining said assemblies together into a portable unit, each of said pair of assemblies consisting of a permanent magnet having an axial bore, a conductor rod with a contact point at one end thereof movably housed in said axial bore of said magnet, and an insulating sleeve encasing said magnet whereby each assembly with the conductor rod therein is electrically isolated from the other, the conductor rods being interconnected into said series circuit for completion thereof through said charged body for the electrical grounding thereof upon contact therewith by said means for attachment through the contact points on said conductor rods, resilient means mountedv between each respective rod and magnet urging each point into contact with said charged body.

References Cited by the Examiner UNITED STATES PATENTS 1,397,290 11/1921 Nelson. 1,519,018 12/1924 Boudreau. 1,768,003 6/1930 Roth. 2,234,982 3/1941 Ross 339-12 X 2,287,112 6/1942 Lourie 33912 2,437,633 3/1948 Abram 33912 FOREIGN PATENTS 617,057 11/1926 France.

540,690 10/1941 Great Britain.

552,378 4/1943 Great Britain.

JOSEPH D. SEERS, Primary Examiner.

ALBERT H. KAMPE, Examiner. 

